Plasma arc welding is generally accomplished by placing a welding torch adjacent a workpiece and directing an inert gas across the tip of an electrode provided in the torch body and onto a workpiece. The interaction of the inert gas and hot electrode forms a substantially constricted arc between the tip of the electrode and the workpiece.
In a typical plasma arc welding torch, the electrode is comprised of a refractory material and is mounted in the torch body in thermally and electrically insulated relation therewith. The electrode is enclosed by the torch body and includes a tip positioned in the forward portion of the torch body. The tip is in spaced relation with an exit orifice in the forward portion of the torch body and an electric arc and an inert plasma gas exits the body through this exit orifice to engage the workpiece.
The inert gas (defined herein as orifice gas) acts upon the electric arc present between the electrode and the workpiece to constrict its shape to that of a narrow column. The orifice gas also provides the necessary atmosphere which allows for electrical transfer of the arc across the gap formed between the electrode and the workpiece. In addition, this inert (orifice) gas provides some shielding effect to the molten weld zone as well as penetration control of the arc, depending on the volume of plasma gas flowing through the torch body. However, typically, a greater shielding effect is required and is accomplished by directing additional inert gas (defined herein as shield gas) around the outer surface of the orifice member and across the orifice thereof to provide a total inert atmosphere at the weld zone. This additional inert shield gas may be the same type of inert gas and received from the same source as the plasma gas, if desired. Or, the additional shield gas may be a different or same gas received from a second inert gas source, if desired.
The quality of the constricted plasma arc column depends on the type of inert gas used as the orifice gas, the tip configuration of the electrode, the size, shape and condition of the constricting orifice and the volume of inert gas directed through the orifice.
It has been found, however, that the orifice gas can more effectively concentrate the arc into a denser and more narrow energy column if the orifice gas were provided with a swirling or vortexing motion as it coacts with the arc. This swirling motion allows for a more narrow weld bead and Heat Affected Zone (HAZ) as well as aiding in maintaining symmetry of the dimensional shape of the arc, thereby substantially eliminating asymmetrical weld bead shapes and related defects due to the same. The continuous circular motion imposed upon the arc by the vortexing thereof also decreases electrode and orifice degradation allowing the electrode and orifice to maintain a uniform configuration, thus eliminating arc asymmetry during long duration welding processes. Averting arc asymmetry also permits the torch to be less operator dependent and reduces or eliminates the need for torch rotation during welding.
The vortexing action of the orifice gas is achieved in the torch of the present invention by providing a swirl ring in the body of the torch. The swirl ring is mounted in an orifice housing member removably secured in the forward portion of the torch body. The orifice housing member is positioned around the electrode adjacent the forward portion thereof and also supports the electrode intermediate the ends thereof and forces the orifice gas passing through the torch body to be directed to an exit orifice of the orifice housing member through a plurality of channels provided on the outer annular peripheral surface of the swirl ring. The channels terminate and mate with angled internal passages provided in the end of the swirl ring to provide the vortexing or swirling motion to the gas at a position adjacent the gas exit orifice of the orifice housing member.
It is, therefore, an object of the present invention to provide an improved plasma arc welding torch.
It is a further object of the present invention to provide such a plasma arc welding torch with an arc shaping device which will maintain symmetry of the electric welding arc and thereby substantially reduce the possibility of asymmetrical weld bead shapes and other related defects which result from asymmetrically shaped arcs.
It is yet a further object of the present invention to provide the torch with such an arc shaping device which may be assembled in and disassembled from the torch body in a rapid and facile manner.
It is still yet another object of the present invention to provide such a welding torch with means for producing a vortexing motion to the inert as the gas leaves the body of the torch whereby the vortexing provides the arc shaping to the electric welding arc.